1. Field of the Invention
This invention relates to sensors for accurately determining the angular position of a high-speed rotating shaft, and to a high performance synchronous drive incorporating such an angular position sensor.
2. Background Information
Many state-of-the-art ac drives, industrial conveyors, positioning systems, and robotic manipulators employ controlled current power electronic converters to realize superior performance. To provide controlled current having precisely defined magnitude and phase related to mechanical position, high resolution position sensing devices are used to provide an appropriate phase reference. Typically, devices such as resolvers, magnetic and optical encoders, hall sensors and such are used for this purpose. There are many applications, however, which could benefit from a more rugged device which could operate at higher speeds, higher temperatures, at higher levels of vibration, and in a polluted environment. One such application is a spray oil cooled variable speed synchronous motor drive which must provide controlled torque from zero to 30,000 rpm at temperatures in excess of 200.degree. C. Such a unit is found in an aircraft generator system in which the generator is operated as a synchronous motor to start the aircraft engine. The devices mentioned above, such as resolvers, magnetic and optical encoders, and hall sensors are not sufficiently rugged for use in such installations. The problem is complicated by the fact that the turbine engine must be capable of being started from a condition in which it is windmilling in the opposite direction.
Typically, aircraft starter generators have a permanent magnet generator which is used as an emergency electric power source and for control power.
It is a primary object of the invention to provide an improved high resolution, high speed rotating shaft position sensor.
It is an additional object of the invention to provide a position sensor which provides accurate position information as the rotating shaft dynamically passes through zero rpm.
It is also a primary object of the invention to provide an improved synchronous ac drive.
It is another object of the invention to provide such a sensor and ac drive which is rugged and reliable under hostile conditions.
It is yet another object of the invention to provide an improved ac drive which can be easily calibrated.